This application relates generally to turbine engines and, more particularly, to methods and apparatus for determining the useful life of turbine engine component coatings.
At least some known turbine engines include a rotor assembly that includes at least one row of circumferentially spaced rotor blades. Each rotor blade includes an airfoil that includes a pressure side and a suction side connected together at axially spaced leading and trailing edges. Each airfoil extends radially outward from a rotor blade platform. Each rotor blade also includes an attachment portion, such as, a dovetail that extends radially inward from the platform, and is used to mount the rotor blade within the rotor assembly to a rotor disk or spool. At least some known rotor disks include a circumferential dovetail slot that is sized to receive the plurality of rotor blades therein. Known rotor blade dovetails are generally shaped complementary to the disk dovetail slot to enable the rotor blade dovetails and the rotor disk slot to mate together and form a dovetail assembly.
To facilitate protecting against high temperature oxidation and hot corrosion, at least some components of gas turbine engines, such as turbine airfoils, are coated with a barrier coating, for example, a diffusion aluminide coating. Diffusion coatings are imparted by a thermal/chemical reaction process and typically require a reduced or inert atmosphere at an elevated temperature. During the coating process, aluminum migrates to the surface of the coating and reacts with air to form a protective alumina coating.
Conventionally, determining the coating life of a gas turbine part involves measuring the remaining amount of beta aluminide in the protective metal coating on the part. However, this method requires local cutting of the component and metallurgical mounting the region of interest so that it can be etched and optically viewed with a microscope to measure the width of the beta aluminide region. The amount of beta aluminide remaining in the coating is indicative of the amount of aluminum remaining for the production of the alumina protective coating, and is thus used to determine coating life. Accordingly, conventional methods destroy the part and are slow and costly. Moreover, field applications require a replacement part.